Chemical characterization of aerosols in the equatorial atmosphere over the Indian Ocean: Fid-Bau Portal

Chemical characterization of aerosols in the equatorial atmosphere over the Indian Ocean

Balasubramanian, Rajasekhar / Karthikeyan, Sathrugnan / Potter, John / Wurl, Oliver / Durville, Caroline

Abstract The region of the Indian Ocean and adjacent countries has received increased attention in recent years in the context of particulate air pollution. Aerosol samples were collected over the equatorial Indian Ocean during a one-year-long sailing cruise that covered the northeast and southwest monsoons, and an inter-monsoon period. The concentrations of airborne particulate matter (PM), selected metals and water-soluble ions were measured. In general, the PM concentrations were influenced by the proximity of sampling locations to land and air mass origins. The enrichment of metals in PM relative to those in the crustal material was very high (up to 40,000). The metal concentrations were significantly higher in PM samples which were influenced by volcanic emissions from the land masses of Indonesia. Volcanic plumes were traced using backward air mass trajectory and chemical tracers, and identified as a major particulate pollution source to the otherwise pristine air of the southern hemisphere of the Indian Ocean. ${NO}_{3}^{-}$ , ${NH}_{4}^{+}$ and ${SO}_{4}^{2 -}$ were low in aerosols collected over the open ocean, but a linear relationship between ${NH}_{4}^{+}$ and ${SO}_{4}^{2 -}$ indicates their importance in the formation of cloud condensation nuclei.

Highlights ► Particulate samples were collected during the course of a year-long sailing cruise across the Indian Ocean. ► The concentrations of selected metals and water-soluble ions were measured. ► Metal concentrations were influenced by volcanic emissions from the land masses of Indonesia. ► Overall, the air masses collected south of the equator were found to be polluted.